Why are my creases horizontal instead of vertical in the sculpt mode?
My first guess would be that you don't have enough geometry in your couch. If all of your polygons are long, thin, horizontal polys, then that's going to affect the way it looks.

There are two ways to solve this problem. One is to manually add more geometry. You want the density the polygons to be the same across the whole couch, and you want them to all be as square as possible. Insert Edge Loops (ctrl+r) will probably be very helpful if you decide to try this approach.

The other solution is to use Dynamic Topology. This will dynamically add geometry as needed, but it will still have an easier time if your geometry is even and consistent.

From the Manual: 


  Dynamic topology (AKA dyntopo) is a dynamic tessellation sculpting method, adds and removes details on the fly. Dyntopo is quick, just get a brush and start to sculpt. Dyntopo will add details base upon your brush size, detail type and strength.